Various types of electrically actuable cylinder plug blocking devices are known to the art.
For instance, U.S. application Ser. No. 3,241,344 (Peters) discloses a key-activated cylinder lock which is intended to secure a deck lid, for instance, and which can also be activated electrically. This lock arrangement includes two mutually independent actuable locking devices which coact in a locked state but which can be actuated selectively and alternatively to open the lock. To this end, there is used a blocking element which is activated by an electromagnet or solenoid and which also coacts with a key-activated side-bar. The blocking element has a pointed end and engages with an obliquely positioned hook in the cylinder plug periphery, in the region of the side-bar. The cylinder lock can be opened by turning the key, whereupon the side-bar is withdrawn and the pointed end of the blocking element is displaced radially inwards while engaging the hook as the cylinder plug is turned against the action of a spring. The lock can also be opened by energizing the electromagnet, whereupon the blocking element shaft, which forms the electromagnet armature, is drawn into the coil so that the plug can be freely rotated.
CH-A-653,400 (Bauer Kaba) discloses a cylinder lock which includes an electromagnetically activated and axially movable side-bar which is mounted in a slot or recess in the end of the cylinder plug located outside the lock housing. When the side-bar is located in an axial position, the plug can be rotated by means of the key, whereas in another axial position the side-bar is accommodated in a recess which prevents the plug from being turned. EP-O 278,906 (Berchtold) discloses an electromagnetic cylinder lock provided with a key which is coded both electronically and mechanically. Electronic elements in the form of a microswitch and an electromagnet with armature are provided. The armature is movable in the direction of its long axis and forms part of a latching device which engages in the cylinder plug through the medium of a release pin and a particularly configured tumbler pin. Located parallel with the release pin is a latching pin which engages in the plug and also in the armature. In order to open the lock, it is necessary for the mechanical latching pin of the lock and also the microswitch, the release pin, the armature and the latching pin to be located in their correct positions.
This cylinder lock is comparatively complicated and its latching elements are comprised of radially movable pins of round cross-section. The electromagnet armature, which can be moved axially, is located at a not inconsiderable distance from the plug and the cylinder has relatively large dimensions, so as to be able to accommodate all components. The actual electromagnet armature has a complicated construction and includes several different grooves and recesses.
EP-A1-0 453,878 (BKS) describes a lock plunger which includes tumblers and an electromagnetic locking function A radially directed side-bar is spring-biassed outwardly to a release position. The head of the electromagnet armature lies against the side-bar and the armature is also urged radially outwards by means of a spring. When the electromagnet is energized, the armature is moved towards the cylinder plug and holds the side-bar in its latching position.
Thus, in this case, the lock includes a radially extending latching element, i.e. a latching element without axial extension which is activated by a radially directed electromagnet--for instance similar to the latching element in the arrangement disclosed in U.S. application Ser. No. 3,241,344.
The patent specification also discloses how to prevent the electromagnet from being rendered non-functional electrically by unauthorized persons attempting to open the lock.
Similar lock structures are described in EP-A2-0 281 507 (Zeiss Ikon) and EP-A1-0 303 849 (BKS).
In all of the aforedescribed lock plugs or cylinders, the plug is blocked electromagnetically by radially directed elements, primarily different types of pins which prevent the plug from being turned.
Locks of this kind are normally relatively easy to force. Another method of forcing such a lock is to use violence, such as to subject the pins to shear forces at the interface between plug and lock cylinder. The latching pins or like devices will fracture even when only a relatively moderate force is used on the lock, therewith enabling the lock to be opened.